Induction motor flux and torque control

Abstract

An induction motor controller is provided. The induction motor controller includes a first module that derives a commanded stator voltage vector, in a stator flux reference frame, via a rotor flux regulator loop and a torque regulator loop, which process at least partially in the stator flux reference frame. The induction motor controller includes a second module that processes the commanded stator voltage vector to produce AC (alternating current) power for an induction motor.

What is claimed is: 
     
       1. An induction motor controller, comprising:
 a controller, configured to couple to one or more sensors and an induction motor having a stator and a rotor, the controller having a first module and a second module; 
 the first module derives a commanded stator voltage vector, in a stator flux reference frame, via a rotor flux regulator loop and a torque regulator loop, which process at least partially in the stator flux reference frame; and 
 the second module processes the commanded stator voltage vector to produce AC (alternating current) power for the induction motor. 
 
     
     
       2. The induction motor controller of  claim 1 , wherein:
 the second module transforms the commanded stator voltage vector from the stator flux reference frame to a phase voltage reference frame, applying vector rotation according to a stator flux angle; 
 the second module generates pulse width modulation switching controls for a DC (direct current) to AC inverter from the commanded stator voltage vector as transformed to the phase voltage reference frame; and 
 the second module generates three-phase AC power for the induction motor from the pulse width modulation switching controls. 
 
     
     
       3. The induction motor controller of  claim 1 , further comprising:
 a third module that produces a torque, a stator flux angle, a rotor flux, a stator current vector expressed in the stator flux reference frame, and a rotor current vector expressed in the stator flux reference frame, from a stator voltage vector expressed in a phase voltage reference frame, a stator current of at least two phases, and a rotational speed of a rotor of the induction motor. 
 
     
     
       4. The induction motor controller of  claim 3 , wherein:
 the rotor flux is coupled from the third module to a flux regulator of the first module; 
 the torque is coupled from the third module to a torque regulator of the first module; 
 the stator flux angle is coupled from the third module to the second module; 
 the stator voltage vector expressed in the phase voltage reference frame is produced by the second module from the commanded stator voltage vector expressed in the stator flux reference frame; and 
 the stator current of at least two phases is provided by the second module. 
 
     
     
       5. The induction motor controller of  claim 1 , further comprising:
 a third module that applies a rotor flux current model and a rotor flux voltage model to generate a rotor flux and a torque, wherein the rotor flux regulator loop includes the rotor flux as an input to the first module, and the torque regulator loop includes the torque as an input to the first module. 
 
     
     
       6. The induction motor controller of  claim 1 , further comprising:
 a fourth module that generates a commanded torque and a commanded rotor flux, limiting the commanded torque to less than or equal to a maximum commanded torque and limiting the commanded rotor flux to greater than or equal to a minimum commanded rotor flux and less than or equal to a maximum commanded rotor flux, the commanded torque and the commanded rotor flux coupled as inputs to the first module. 
 
     
     
       7. The induction motor controller of  claim 1 , wherein:
 the first module includes a torque regulator that processes a portion of the torque regulator loop and produces a projection of the commanded stator voltage vector onto a quadrature axis in the stator flux reference frame; and 
 the first module includes a rotor flux regulator that processes a portion of the rotor flux regulator loop and produces a projection of the commanded stator voltage vector onto a direct axis in the stator flux reference frame. 
 
     
     
       8. An induction motor controller, comprising:
 a controller, having a torque regulator, a rotor flux regulator and a stator flux reference frame to phase voltage reference frame vector rotation module, the controller configured to couple to at least one sensor and an induction motor having a stator and a rotor; 
 the torque regulator processes in a stator flux reference frame a commanded torque, a torque, a commanded rotor flux, and a rotational speed of a rotor of an induction motor, to produce a commanded stator voltage projected onto a quadrature axis in the stator flux reference frame; 
 the rotor flux regulator processes in the stator flux reference frame the commanded rotor flux and a rotor flux, to produce the commanded stator voltage projected onto a direct axis in the stator flux reference frame; and 
 the stator flux reference frame to phase voltage reference frame vector rotation module applies a stator flux angle to transform the commanded stator voltage, as projected onto the direct axis and the quadrature axis, from a first vector expressed in the stator flux reference frame to a second vector expressed in the phase voltage reference frame. 
 
     
     
       9. The induction motor controller of  claim 8 , further comprising:
 a flux and torque estimator that generates the stator flux angle, the rotor flux, the torque, a rotor current vector expressed in the stator flux reference frame, and a stator current vector expressed in the stator flux reference frame, from a stator voltage vector expressed in the phase voltage reference frame, a stator current of at least two phases, and the rotational speed of the rotor; and 
 the flux and torque estimator including a phase voltage reference frame to stator flux reference frame vector rotation module that transforms current vectors from the phase voltage reference frame to the stator flux reference frame. 
 
     
     
       10. The induction motor controller of  claim 8 , further comprising a flux and torque estimator that includes:
 a stator phase current reference frame to phase voltage reference frame vector rotation module that transforms a stator current of at least two phases to a stator current vector expressed in the phase voltage reference frame; 
 a rotor flux current model that generates a first rotor flux vector expressed in the phase voltage reference frame from the stator current vector expressed in the phase voltage reference frame and the rotational speed of the rotor; 
 a rotor flux voltage model that generates a second rotor flux vector expressed in the phase voltage reference frame from a stator voltage vector expressed in the phase voltage reference frame, the stator current vector expressed in the phase voltage reference frame, and an estimation correction factor; 
 an estimator regulator that generates the estimation correction factor from the first rotor flux vector expressed in the phase voltage reference frame and the second rotor flux vector expressed in the phase voltage reference frame; 
 a rotor flux magnitude calculator that generates the rotor flux from the first rotor flux vector expressed in the phase voltage reference frame; 
 a stator flux calculator that generates a stator flux vector expressed in the phase voltage reference frame from the second rotor flux vector expressed in the phase voltage reference frame and the stator current vector expressed in the phase voltage reference frame; 
 a rotor current calculator that generates a rotor current vector expressed in the phase voltage reference frame from the first rotor flux vector expressed in the phase voltage reference frame and the stator flux vector expressed in the phase voltage reference frame; 
 a torque calculator that generates the torque from the stator current vector expressed in the phase voltage reference frame and the stator flux vector expressed in the phase voltage reference frame; 
 a stator flux angle calculator that generates the stator flux angle from the stator flux vector expressed in the phase voltage reference frame; and 
 a phase voltage reference frame to stator flux reference frame vector rotation module that generates the rotor current vector expressed in the stator flux reference frame and the stator current vector expressed in the stator flux reference frame, from the rotor current vector expressed in the phase voltage reference frame, the stator current vector expressed in the phase voltage reference frame, and the stator flux angle. 
 
     
     
       11. The induction motor controller of  claim 10 , wherein:
 the estimator regulator includes a PI (proportional-integral) controller; 
 the stator flux calculator includes a model of inductances for windings of the induction motor; 
 the stator flux reference frame to phase voltage reference frame vector rotation module performs a second transformation that is an inverse of a first transformation performed by the phase voltage reference frame to stator flux reference frame vector rotation module; and 
 each of the rotor flux current model, the rotor flux voltage model, the rotor flux magnitude calculator, the rotor current calculator, the stator flux calculator, the torque calculator and the stator flux angle calculator is lookup-table-based or real-time-calculation-based. 
 
     
     
       12. The induction motor controller of  claim 8 , further comprising:
 a space vector modulation module that generates pulse width modulation (PWM) switching controls, and generates a stator voltage vector expressed in the phase voltage reference frame, from the commanded stator voltage received as the second vector and a DC (direct current) voltage of a power source; and 
 a DC to AC (alternating current) inverter that generates three-phase AC power for the induction motor from the PWM switching controls. 
 
     
     
       13. The induction motor controller of  claim 8 , further comprising:
 a flux and torque limiter that generates a minimum commanded rotor flux, a maximum commanded rotor flux, and a maximum commanded torque, from a stator current vector expressed in the stator flux reference frame, a rotor current vector expressed in the stator flux reference frame, an inverter temperature, a motor temperature, and the rotational speed of the rotor. 
 
     
     
       14. The induction motor controller of  claim 8 , further comprising a flux and torque limiter that includes:
 a rotor current limiter that generates a maximum rotor current from the rotational speed of the rotor, a rotor current vector expressed in the stator flux reference frame, and a motor temperature; 
 a field weakener that generates a maximum stator flux from the rotational speed of the rotor and a DC (direct current) voltage of a power source; 
 a stator current limiter that generates a maximum stator current from the rotational speed of the rotor, a stator current vector expressed in the stator flux reference frame, and an inverter temperature; 
 a low rotor flux limiter that generates a minimum commanded rotor flux from the maximum rotor current and the rotational speed of the rotor; 
 a high rotor flux limiter that generates a maximum commanded rotor flux from the maximum stator flux and the maximum stator current; 
 a stator-based torque limiter that generates a maximum stator-based commanded torque from the maximum stator flux and the maximum stator current; 
 a rotor-based torque limiter that generates a maximum rotor-based commanded torque from the maximum rotor current and the maximum commanded rotor flux; and 
 a final torque limiter that generates a maximum commanded torque from the maximum rotor-based commanded torque and the maximum stator-based commanded torque; 
 wherein each of the rotor current limiter, the field weakener, the stator current limiter, the low rotor flux limiter, the high rotor flux limiter, the stator-based torque limiter, and the rotor-based torque limiter is lookup-table-based or real-time-calculation-based. 
 
     
     
       15. The induction motor controller of  claim 8 , further comprising a flux and torque limiter that includes:
 a rotor current limiter that decreases a maximum rotor current in response to an increased motor temperature; 
 a field weakener that decreases a maximum stator flux in response to the rotational speed of the rotor exceeding a base speed and further decreases the maximum stator flux in response to a decreasing DC (direct current) voltage of a power source; 
 a stator current limiter that decreases a maximum stator current in response to an increased inverter temperature; 
 a low rotor flux limiter that sets a minimum commanded rotor flux consistent with readiness to accelerate the rotor; 
 a high rotor flux limiter that sets a maximum commanded rotor flux based upon the maximum stator flux and the maximum stator current; 
 a stator-based torque limiter that sets a maximum stator-based commanded torque based upon a product of the maximum stator flux and the maximum stator current; 
 a rotor-based torque limiter that sets a maximum rotor-based commanded torque based upon a product of the maximum rotor current and the maximum commanded rotor flux; and 
 a final torque limiter that sets a maximum commanded torque selected as a lesser of the maximum rotor-based commanded torque and the maximum stator-based commanded torque. 
 
     
     
       16. The induction motor controller of  claim 8 , further comprising:
 a torque command generator that generates the commanded torque from a maximum commanded torque and an initial commanded torque, the maximum commanded torque applied to the initial commanded torque as a torque limit; and 
 a rotor flux command generator that generates the commanded rotor flux from a minimum commanded rotor flux, a maximum commanded rotor flux, and the commanded torque, the minimum commanded rotor flux and the maximum commanded rotor flux applied to the commanded rotor flux as flux limits. 
 
     
     
       17. The induction motor controller of  claim 8 , wherein:
 the torque regulator includes a proportional-integral (PI) controller having a difference between the commanded torque and the torque as an input; and 
 the torque regulator includes a feedforward summation having as inputs an output of the PI controller and a product of the commanded rotor flux and the rotational speed of the rotor, the feedforward summation having as an output the commanded stator voltage projected onto the quadrature axis in the stator flux reference frame. 
 
     
     
       18. The induction motor controller of  claim 8 , wherein:
 the rotor flux regulator includes a proportional-integral-derivative (PID) controller having as inputs the commanded rotor flux and the rotor flux, and having as an output the commanded stator voltage projected onto the direct axis in the stator flux reference frame. 
 
     
     
       19. A controller-based method of controlling an induction motor, comprising:
 generating a stator voltage vector, in a stator flux reference frame, the generating including,
 generating a quadrature axis projection of a commanded stator voltage vector expressed in the stator flux reference frame from a commanded torque, a torque, a commanded rotor flux, and a rotational speed of a rotor of the induction motor; and 
 generating a direct axis projection of the commanded stator voltage vector expressed in the stator flux reference frame from the commanded rotor flux and a rotor flux, wherein the stator voltage vector, in the stator flux reference frame, includes the direct axis projection of the commanded stator voltage vector and the quadrature axis projection of the commanded stator voltage vector; 
 
 transforming the stator voltage vector from the stator flux reference frame to a phase voltage reference frame; and 
 producing alternating current (AC) power for an induction motor, from the stator voltage vector of the phase voltage reference frame, wherein at least one step of the method is performed by a processor. 
 
     
     
       20. The method of  claim 19 , wherein generating the quadrature axis projection of the commanded stator voltage vector expressed in the stator flux reference frame includes:
 subtracting the torque from the commanded torque to form a torque error; 
 adding a first term proportional to the torque error and a second term proportional to an integral of the torque error to form a PI (proportional-integral) controller output; 
 multiplying the rotational speed of the rotor by the commanded rotor flux to form a feedforward quantity; and 
 adding the feedforward quantity to the PI controller output to form the quadrature axis projection of the commanded stator voltage vector expressed in the stator flux reference frame. 
 
     
     
       21. The method of  claim 19 , wherein generating the direct axis projection of the commanded stator voltage vector expressed in the stator flux reference frame includes:
 subtracting the rotor flux from the commanded rotor flux to form a flux error; and 
 adding a first term proportional to the flux error, a second term proportional to an integral of the flux error, and a third term proportional to a derivative of the flux error to form the direct axis projection of the commanded stator voltage vector expressed in the stator flux reference frame.